1. Field of the Invention
The present invention relates to a mechanical seal member excellent in wear resistance and penetration resistance, capable of stably maintaining a slide sealing effect for a long duration, and usable for a widely employed pump for a refrigerator, an automotive water pump, and the like.
2. Description of the Prior Art
In the recent years, while a graphitic carbon material has widely been used as a mass production type and miniaturized mechanical seal member for a widely usable pump for such as a refrigerator, an automotive water pump, and the like, it is required to further improve the characteristics such as a higher slurry resistance, a higher peripheral speed, a longer life, a higher blister resistance, and so forth.
Hence, as a material to satisfy these requirements, Japanese Patent Application Laid-Open No. Hei 10(1998)-53480 has disclosed a technique of providing a mechanical seal member by applying a silicon paste to the surface layer including a sliding face of a carbon substrate and conversing the silicon paste into a silicon carbide-based substance.
However, silicon is difficult to penetrate carbon if the pore radius is 1 xcexcm or smaller. For that, even if penetration takes place owing to capillarity, it is limited and reaches at deepest about 1 to 2 mm and therefore the thickness of a carbon-silicon carbide composite layer formed by thermal treatment is at thickest about 2 mm. Further, there occurs a problem that the penetration in the inside is not even and that the thickness of the formed carbon-silicon carbide composite layer is uneven.
Therefore, since the thickness of the formed composite layer partly differs, a product is sometimes strained owing to the partial difference of the thermal expansion coefficient of the layer from that of the carbon substrate to make it necessary to subject the product to machining to a proper product size after the carbon-silicon carbide composite layer formation.
The purpose of the present invention is to provide a mechanical seal member for a small size and widely usable pump which is excellent in slide sealing property, blister resistance, and machining to a product size aside from last abrasion processing of a sliding respect becoming unnecessary by evenly forming a carbon-silicon carbide composite layer deep from the surface and on the whole face of the product.
A mechanical seal member relevant to the present invention is provided with a carbon-silicon carbide composite layer in the whole surface by providing some catalytic function or other by adding boron carbide in order to achieve the foregoing purpose. That is a slurry containing a boron carbide powder and a silicon powder mixed and dispersed therein is applied to the whole surface of a carbon material processed to have a product shape by machining a hollow tubular or cylindrical carbon material having pores with 1.0 xcexcm larger average fine pore radius and the applied slurry is fired to form a carbon-silicon carbide composite substance in the whole surface area of the foregoing carbon material with a product shape toward inner side and to form a thin coating of 3 to 30 xcexcm containing silicon carbide and boron carbide as main components in the surface to obtain a mechanical seal member. Further, since the mechanical seal member is not larger than 7xc3x977 mm in cross-section surface area parallel to the center axis, the carbon-silicon carbide composite substance is approximately evenly formed toward inside from the surface in the depth direction and the carbon-silicon carbide composite substance reaches approximately the center part of the foregoing cross-section. The siliconizing ratio of the surface of the carbon-silicon carbide composite material is 30 to 55% by surface area. The density of the carbon substrate to be used is 1.7 g/cm3 or higher and the density after siliconization is 2.0 to 2.5 g/cm3. Further, the pores of the carbon-silicon carbide composite material may be impregnated with a metal or a resin to be a mechanical seal member.